samples/Wiktionary/res/drawable/progress_spin.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (C) 2009 The Android Open Source Project

     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

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     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
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<rotate xmlns:android="http://schemas.android.com/apk/res/android"
        android:pivotX="50%"
        android:pivotY="50%"
        android:fromDegrees="0"
        android:toDegrees="360">

    <shape
        android:shape="ring"
        android:innerRadiusRatio="4"
        android:thicknessRatio="5.333"
        android:useLevel="false">

        <size
            android:width="18dip"
            android:height="18dip" />

        <gradient
            android:type="sweep"
            android:useLevel="false"
            android:startColor="#006688cc"
            android:centerColor="#886688cc"
            android:endColor="#ff6688cc"
            android:centerY="0.50" />

    </shape>

</rotate>